This invention relates to nickel base superalloy materials having improved strength and stabilization. More particularly, it relates to the strengthening and stabilization of the superalloys by uniform dispersion of metal nitride phases.
"Superalloys" is a generic name given to certain nickel base alloys having a unique microstructure. The alloys are further characterized by their heat resistance and high strength. These alloys generally contain from about 50 to about 75 weight percent of nickel alloyed with varying amounts of chromium, cobalt, aluminum, titanium, molybdenum, tungsten, niobium, tantalum, boron, zirconium and carbon. The metallurgical composition of superalloys are known such as those compiled in the ASTM Subcommittee XII Report, published by the Metal Processing Division of Curtiss-Wright Corporation. In the 8th edition of the Metals Handbook "Superalloys" are defined as alloys developed for high temperature service where relative high stresses (tensile, thermal, vibratory and shock) are encountered and where oxidation resistance is frequently required, and is the definition used herein. Typical alloys are supplied by a variety of suppliers under tradenames of IN-100, Astroloy, etc.
The prior art teaches that superalloys can be strengthened and stabilized by solid solution methods and by the formation of fine carbides from the elements of titanium, zirconium, tantalum, columbium, molybdenum, tungsten and chromium. Other materials which strengthen and stabilize superalloys are oxide dispersions such as alumina and yttria. The disadvantages of carbide strengthened alloys are that due to the carbide overaging deterioration of ductility occurs. Additionally, unless there is a uniform distribution of the carbides throughout the superalloy there is nonuniform ductility. The oxide dispersed superalloys have a critical manufacturing technique which is expensive and time consuming. Additionally, there can be undesired effects such as large dispersoids, excessive oxygen content and impurities which can be introduced during the manufacturing. These effects result in undesired changes in certain properties of the superalloys.
U.S. Pat. No. 3,591,362, issued July 6, 1971, describes a process for producing various dispersion strengthened materials via a process in which a "dispersed" phase in a compound form is mechanically beaten into the parent or host metal. While the milling procedure disclosed therein has advantages in producing many products, the degree of dispersion is dependent upon energy input. As a result energy requirements are high and uniformity of dispersion varies with the amount of dispersed phase employed. Addtitionally, the process requires a distinct compound for each dispersant. In addition, the product is dependent upon the original particle size of the dispersed material. In some instances it is impossible to achieve submicron size compounds for dispersion into the present metal.
It is believed, therefore, that a superalloy having a desired strengthening and stabilization additive which overcomes the disadvantages present in the prior art compositions, is an advancement in the art. Further, it is believed that a process which enables the production of such alloys in a simple manner is a further advancement in the art.